Surfactant protein B inhibits secretory phospho-lipase A_2 hydrolysis of surfactant phospholipids.

摘要

Hydrolysis of surfactant phospholipids (PL) by secretory phospholipases A_2 (sPLA_2) contributes to surfactant damage in inflammatory airway diseases such as acute lung injury/acute respiratory distress syndrome. We and others have reported that each sPLA_2 exhibits specificity in hydrolyzing different PLs in pulmonary surfactant and that the presence of hydro-philic surfactant protein A (SP-A) alters sPLA_2-mediated hydrolysis. This report tests the hypothesis that hydrophobic SP-B also inhibits sPLA_2-mediated surfactant hydrolysis. Three surfactant preparations were used containing varied amounts of SP-B and radiolabeled tracers of phosphatidylcholine (PC) or phosphatidylglycerol (PG): 1) washed ovine surfactant (OS) (pre- and postorganic extraction) compared with Survanta (protein poor), 2) Survanta supplemented with purified bovine SP-B (1-5%, wt/wt), and 3) a mixture of dipalmitoylphos-phatidylcholine (DPPC), 1 -palmitoyl-2-oleoyl-phosphatidylcholine (POPC), and l-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) (DPPQPOPGPOPG, 40:40:20) prepared as vesicles and monomo-lecular films in the presence or absence of SP-B. Hydrolysis of PG and PC by Group IB sPLA_2 (PLA2G1A) was significantly lower in the extracted OS, which contains SP-B, compared with Survanta (P = 0.005), which is SP-B poor. Hydrolysis of PG and PC in nonextracted OS, which contains all SPs, was lower than both Survanta and extracted OS. When Survanta was supplemented with 1% SP-B, PG and PC hydrolysis by PLA2G1B was significantly lower (P < 0.001) than in Survanta alone. When supplemented into pure lipid vesicles and monomolecular films composed of PG and PC mixtures, SP-B also inhibited hydrolysis by both PLA2G1B and Group IIA sPLA2 (PLA2G2A). In films, PLA2G1B hydrolyzed surfactant PL monolay-ers at surface pressures approx=30 mN/m (P < 0.01), and SP-B lowered the surface pressure range at which hydrolysis can occur. These results suggest the hydrophobic SP, SP-B, protects alveolar surfactant PL from hydrolysis mediated by multiple sPLA_2 in both vesicles (alveolar subphase) and monomolecular films (air-liquid interface).